For questions 1-10 on high school tests, the most common concept we haven't covered yet is dividing decimals. It has appeared 6 times so far this year, with a median placement at question # 8.
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Number Dojo Level: 85
When dividing by decimals, I choose to eliminate them altogether before dividing. Here's how:
- Count the decimal places in both the dividend and the divisor. Note how many decimal places are in each, and choose the higher number (of decimal places).
- Move the decimal that many places to the right in both the dividend and the divisor.
- Divide the (now) whole numbers.
Example 1: 30.6 ÷ .4 = ___ decimal
- There is one decimal place in each number. Move the decimal once to the right.
- The problem becomes 306 ÷ 4, which is 76.5
Example 2: 31.5 ÷ .09 = ___
- There is one decimal place in the dividend, but two in the divisor. Move the decimal twice to the right.
- The problem becomes 3150 ÷ 9, which is 350.
Example 3: .1236 ÷ .06 = ___ decimal
- There are 4 decimal places in the dividend, so move the decimal 4 times to the right in each number.
- The problem becomes 1236 ÷ 600, which is 2.06
Example 4: 3.636 ÷ .12 = ___
- Move the decimal 3 times to the right in each number.
- The problem is now 3636 ÷ 120, which is 30.3
Example 5: 22.5 ÷ 0.03 = ___
- Move the decimal twice to the right in each number.
- The problem is now 2250 ÷ 3, which is 750.